The present invention includes a method and apparatus for cutting creasing and/or embossing of stock in sheet or web form, of paper, cardboard or similar material by the combined action of two surfaces.
The method of the present invention is to be used preferably to make folding boxes or similar work pieces.
To date, such work pieces were blanked almost exclusively with flat strip steel punches. It has also been suggested that a scissor cut between two steel plates with etched surface patterns may be employed (U.S. Pat. No. 3,170,342 and German Pat. No. 1,611,626). Such steel plates have been further modified by recommending a crimping parting cut (German Pat. No. 1,940,830). Both suggestions also provide for the use of such tools for rotational blanking. Attempts have been made to utilize the fundamental advantages of rotational blanking by adapting punching knives formed of known construction (flat strip steel) to the curve of a punching cylinder. To facilitate this adaptation, especially for cutting lines which run at a slant over the cylinder or are curved, other shapes of the knives have been suggested (German Pat. No. 2,032,145 and others).
While the commonly used strip steel punch is inexpensive to make, the correct adjustment of the punch to compensate for unavoidable variations in the measurements of the knives and pressure at the cutting surfaces in automatic punching machines and elastic deformation are very time consuming. Even more time is wasted in the case of a cylindrical tool, since the adaptation of the punching knives to the curve of the cylinder brings additional defects which must be compensated for with additional fitting work.
This fitting work is not necessary if steel plates with etched surface patterns of flat or cylindrical form are used, but high precision in the location of the cutting lines is required when the combined action of pairs of punches is to be employed, creating yet further difficulties. In addition to the other disadvantages, the higher price of these tools speaks against their being widely used.
It is the purpose of this invention to provide a method for blanking stock in sheet or web form, of paper, cardboard or similar material, using a tool which is inexpensive to make and can be used flat or in cylindrical form without requiring adjustment of the cutting lines.
According to the present invention the problem has been solved by providing a first surface at the parting lines of the stock with rigid steps, while a second surface is made of softer, preferably elastic material, whereby each of said surfaces may be flat or cylindrical.
As soon as a sufficient force presses both surfaces towards each other, the stock in between is divided at the steps, whereupon the elastic of the two surfaces assumes the shape of the stepped surface.
If both surfaces are flat, the entire form is parted.
If one surface is cylindrical, the action of the force is limited to a narrow zone which progresses with the revolution of the cylinder and the roller movement between the cylinder and flat surface over the length of the sheet.
If both surfaces are cylindrical, the action of the force is limited to a narrow zone which progresses with the revolution of boty cylinders over the length of the sheet, such revolution also conveying the stock between the cylinders.
One important embodiment of said invention includes negative or positive creasing elements in the form of grooves or ribs arranged in the first plate. This produces creases in a single operation with the parting or cutting of the work pieces, whereby the stock is formed by pressing the elastic surface into the groove or around the ribs.
A further supplement to this embodiment of said invention consists in equipping the first plate with negative or positive coining dies. This makes it possible in a single operation, to not only blank and crease, but also coin the work pieces, since the elastic surface presses the stock into the coining die.
Another embodiment of the invention calls for the die steps to be made by tooling or machining of a plate, which plate can be used with a flat, curved or cylindrical blanking apparatus.
Still another embodiment of the invention calls for the die steps to be made by mounting elements on a plate, which plate can be used with a flat, curved or cylindrical blanking apparatus.
A further embodiment of said invention calls for the die steps to be formed by tooling or machining of a cylinder.
In a fourth embodiment of said invention the steps are formed by mounting elements on a cylinder.
The first two embodiments are particularly inexpensive in their manufacture, so that they are recommended for use with a large number of frequently changed patterns. The latter two embodiments are recommended mainly for mass production of one pattern over a long period of time. It is also possible to combine the formation of the die steps by tooling and by mounting of elements in one and the same tool.
For certain applications it is advisable to form the die steps at varying distances from the base of the flat plate or center of the cylinder. This arrangement makes it possible to blank areas of the stock in which more than two different parts touch, e.g., two work pieces and one waste piece.
It is advantageous that elastic waste ejector elements are arranged on the lower areas of the plate or cylinder. It is also possible to feed compressed air to the lower areas of the plate or cylinder. Each of the two last-mentioned measures will result in raising of the material parts which were pressed by the blanking process into the recesses formed by the steps, as soon as the two die surfaces part after the blanking process.
It is advantageous to coat the elastic surface with a material of low friction value. The stretching caused by deformation of the elastic surface results in local displacements or relative movement between the surface of the stock and the elastic surface. By lowering the friction value, the thus created friction stress is lowered.
The elastic surface can be limited in shape or effect to the areas of stock to be worked. This will reduce the force needed to compress the two areas, since the force required for blanking per surface unit need be provided for only a small area.
The invention provides the following advantages: The precision with which the die set is to be made, is determined only by the requirements of work pieces to be made. The process itself does not require any special precision, either as to flatness or as to cylindrical form, nor for the position of the cutting lines with respect to each other. The combined action of pairs of tool elements is eliminated. This also applies to the creasing lines which consist of negative and positive elements in the commonly used strip steel punch. In that case they must be adjusted with precision, otherwise unilateral or slanted creases will result, which disturb the further forming of the box forms in the pasting and packing machines.
It is no longer necessary to adjust the cutting lines, and this results first of all in a considerable time saving during each change of pattern. Additionally, there is not time-consuming checking and supplementing of the punch adjustment during blanking.
These advantages make the process of the present invention superior in its use over common automatic punching machines with flat tools. Even greater economic savings are attained if the process is used with rotating punching machines which permit much higher stock speeds. These machines are also more economical in their production than the punching machines with flat tools, so that the invention will result in a considerable lowering of manufacturing costs for folding boxes and similar work pieces.